Development of a Three-Dimensional Bird's-eye View Map Drawing Technique for Car Navigation Systems

In this paper, a newly developed three-dimensional (3D) bird's-eye view map drawing technique for car navigation systems is described. Conventional navigation systems give pseudo-perspective views which can not express ruggedness like hills and valleys. Our newly developed navigation system can display undulation of the land from viewpoints above and behind the current position, so that ups and downs of roads along with the driver's destination can be seen easily. The 3D-road map is not only effective during navigation but also during route planning, because it assists in searching for fine views before travel.

In order to achieve the 3D-map view, we developed graphics software libraries, which work on a 32-bit RISC processor and on a low-cost graphics accelerator LSI with texture mapping capability. The graphics software libraries are constructed with three stages, the perspective projection stage, visible-surface determination stage, and rendering stage. In the perspective projection stage, 3D objects are projected onto a two-dimensional projection plane quickly. In the visible-surface determination stage, the background rectangles generated by the digital elevation model and polyline data of the road map are selected in the order of row-by-row or column-by-column so that a simple painter's algorithm can be applied. This algorithm can be implemented without additional memories or specialized hardware. In the rendering stage, the background rectangles are rendered by the determined color based on height. To eliminate intensity discontinuities at the rectangle edge, the background rectangles are shaded smoothly. This process is implemented by using texture mapping which works on the graphics accelerator LSI quickly.